Depending on where you are in the Bay Area, you can actually go to the Grist Mill in St. Helena and get it freshly ground by the miller. I believe it's one of the few running mills left in the states. Kind of random but lots of fun.

I stop by while I'm up there a few times a year and stock up. The miller grinds cornmeal, polenta, flour etc. Definitely the best quality around, and it's technically free, they just ask for donations. Several of the local restaurants in the valley serve it on their menus.